The present invention relates to an inspection system for sampling and determining the presence of certain substances, such as residues of contaminants within plastic materials to be recycled from containers such as plastic polyethylene terephthalate (PET) beverage bottles or plastic food containers. More specifically, the present invention relates to an improved sampling and analyzing system and method for determining the presence of substances such as residues of contaminants in plastic materials from recycled articles such as beverage bottles or other containers--e.g., as the material is rapidly moved along a conveyor past a series of test stations in a material washing and sorting system.
In many industries, including the beverage industry, products are packaged in containers which are returned after use, washed and refilled. Typically refillable containers, such as beverage bottles, are made of glass which can be easily cleaned. These containers are washed and then inspected for the presence of foreign matter.
Glass containers have the disadvantage of being fragile and, in larger volumes, of being relatively heavy. Accordingly, it is highly desirable to use plastic containers because they are less fragile and lighter than glass containers of the same volume. However, plastic materials can absorb a variety of compounds which may later be desorbed into the product thereby potentially adversely affecting the quality of the product packed in the container. Examples of such compounds include but are not limited to ammonia, organic nitrogenous compounds, and hydrocarbons including gasoline and various cleaning fluids including soaps and detergents.
However, if these plastic containers, or the materials from which each is made can be reliably inspected for contaminants of very high sensitivity, contaminated plastic bottles or materials can be separated from uncontaminated containers or materials, and the good containers or materials can be recycled.
The aforementioned U.S. application Ser. No. 07/890,863 describes inspection techniques for determining the presence of contaminants in used, plastic beverage containers, or in shredded or flaked plastic material from which the containers were made.
The present invention is directed to improvements to the techniques described in the prior application Ser. No. 07/890,863 regarding recycling of plastic materials, including materials from which such used plastic beverage containers were made.
In order to recycle plastic materials such as from PET beverage bottles for use in the fabrication of new bottles, it is necessary to ensure that the recycled material does not contain any potentially harmful contaminants of the types described hereinbefore.
While various efforts have been made for removing unwanted contaminated plastics from an incoming stream of beverage bottles, and then shredding the bottles and thoroughly washing the shredded plastic material so as to remove potentially harmful contaminants from the shredded or flaked material, a need in the art exists for improved inspection of recycled plastic materials. In particular, it would be advantageous to have on-line, real-time, chemical monitoring of recycled plastic materials such as bottles or resulting flake at any stage of processing, particularly at any stage of pre-processing, including sortation, cleaning, washing, flaking, pelletizing and preform and/or bottle manufacturing to ensure that badly contaminated material has been removed from the recycled material.